1. Field of the Invention
The present invention relates to a display control apparatus and method and, more particularly, to display control apparatus and method for a display apparatus having, for example, a ferroelectric liquid crystal as an operating medium for updating a display content, in which such a ferroelectric liquid crystal can hold a display state updated by applying an electric field or the like.
2. Related Background Art
Generally, in an information processing system or the like, a display apparatus is used as information display means for performing a visual expressing function of information. A CRT display apparatus is widely known as such a display apparatus.
In a display control in the CRT display apparatus, the writing operation of a CPU on the system side for a video memory as a display data buffer which the CRT side has and the operations to read out the display data from a video memory and to display the display data which are executed by, for example, a CRT controller which the CRT side has are respectively independently executed.
In case of the display control of the CRT as mentioned above, the writing operation of the display data to the video memory for the purpose of a change in display information or the like and the operations to read out the display data from the video memory and to display it are independently executed. Therefore, there is an advantage such that in a program on the information processing system side, there is no need to consider the display timing or the like and desired display data can be written at an arbitrary timing.
On the other hand, since the CRT needs a certain length in the direction of thickness of the display screen in particular, volume of the entire CRT increases and it is difficult to miniaturize the whole display apparatus. Consequently, when the information processing system using such a CRT as a display is used, degrees of freedom, namely, degrees of the installing location, portability, and the like are lost.
A liquid crystal display (hereinafter, referred to as an LCD) can be used as a display which can solve such a drawback. Namely, according to the LCD, the whole display apparatus can be miniaturized (especially, a thickness can be thinned). Among such LCDs, there is a display (hereinafter, referred to as an FLCD: FLC display) using a liquid crystal cell of a ferroelectric liquid crystal (hereinafter, referred to as an FLC: Ferroelectric Liquid Crystal) mentioned above. One of the features of the FLCD is that the liquid crystal cell has a preserving performance of a display state when an electric field is applied. Namely, in the FLCD, the liquid crystal cell is thin enough and an elongated FLC molecule in the liquid crystal cell is oriented in the first or second stable state in accordance with the applying direction of the electric field. Even when the electric field is extinguished, each orienting state is maintained. The FLCD has a memory performance due to such a bistability of the FLC molecule. Such FLC and FLCD have been described in detail in, for example, in U.S. Pat. No. 4,964,699.
Therefore, in case of driving the FLCD, different from the CRT or other liquid crystal displays, there is a surplus time in the continuous refresh driving period of time of the display screen. On the other hand, irrespective of the continuous refresh driving, it is possible to perform a partially rewriting driving to update the display state of only the portion corresponding to the change portion on the display screen.
Therefore, in the FLCD, if the partially rewriting driving can be properly executed at a good timing, the advantage of the FLCD can be further enhanced.
If such an FLCD can be used as a display apparatus of the information processing system so as to have a compatibility with the CRT, a flexibility of the system increases and its value can be raised.
From the above viewpoint, it is possible to consider a display control method whereby the partial rewriting operation of a predetermined portion is preferentially executed than the partial rewriting operation of other display information. As a display example based on such a display control method, there is a display of continuous image data like an animation and such a display needs to visually change the display state in a real-time manner.
In the case where the display data has a density value every pixel of R (Red), G (Green), and B (Blue), it is necessary to convert the display data into the data which can be displayed (expressed) by the FLCD.
In case of using a method (for example, an error diffusion method) whereby errors which occur upon conversion are reflected to the other pixels instead of a method whereby the conversion is independently executed on a pixel unit basis, there is a problem such that it is necessary to take the converting method into consideration in the partially rewriting driving method.
On the other hand, in case of using the FLCD in place of the CRT as a display apparatus of the information processing system having the CRT display, an essential problem occurs from a viewpoint of the construction. That is, the CPU on the system side merely transfers the display data of one image plane regarding the display updating and its addresses to the display apparatus side. There is, accordingly, a problem with respect to how to discriminate the preceding image plane and the changed portion and to execute the partial rewriting operation as mentioned above.